The fogging of surfaces, especially of optical elements, which is caused by condensation effects and precipitating moisture, is problematic in many respects. It is important not only in leisure areas, for example, in sports or in traffic, but also especially in safety engineering products that the operability of the components always be guaranteed. In objects of personal safety gear, for example, the visual capacity may be highly limited due to fogged mask disks, glasses and disks of protective suits due to condensation. As a result of a limited visibility, it could be that rescue operations would have to be interrupted or a fast escape from a life-threatening environment becomes hindered.
Various approaches have already been followed to reduce fogging of a surface. In this connection, mechanical methods, such as heating the disks or installing a wiper in the inner area of disks, are not only technically complicated to manufacture, but also prone to malfunction. In addition, a constant supply of current must be guaranteed so that the effect is maintained.
Furthermore, methods have been described, in which hydrophilic or hydrophobic surface properties are utilized. In multilayer systems as shown in DE 10 2006 008 784 A1 and in EP 0 871 046 A1, a lower hydrophilic, water-storing layer is covered with another mostly hydrophobic layer, which has holes or a porous structure. Moisture reaches the water-storing layer through the cavities and an antifogging effect is achieved.
However, a plurality of layers must be manufactured in a complicated process for this, and the pores or holes are inserted into the surface coating in a specific manner. If the maximum capacity of the water-storing layer is reached, a fogging of the surface occurs nevertheless; thus, the function of the components is only guaranteed in limited areas of application.
Another method for reducing fogging is the coating or the specific preparation of a surface having a hydrophilic character, based on the chemical properties of defined substances. DE 696 26 266 T2 describes the polycondensation of polyacrylic acid compounds with inorganic alkoxides as non-fogging antireflection film. Another example of a hydrophilic coating is disclosed in EP 1 324 078 A2. In this connection, a hydrophilic surface is produced by means of vapor deposition of organic substances with hydrophilic groups together with inorganic oxides.
The drawback of using a hydrophilic surface as an antifogging agent is that the capacity of the water-storing layer, which shall form a thin transparent fluid film, is limited in this case as well. It is also important that the surface coating be uniform and be configured as contiguous. This requires a very precise manufacturing method. In addition, these usually very thin layers do not have a stable enough configuration, so that these layers are worn out and lose their effect in case of mechanical stress, for example, during a cleaning of the components.